It is known to apply arc-lamps in spectrophotometer, reflectometer, ellipsometer, polarimeter or the like systems which direct beams of electromagnetic radiation therefrom to samples at normal or oblique angles-of-incidence. It is further known that arc-lamps generally present with an elongated dimension. Manufacturer recommendation is that arc-lamps be mounted so that their elongated dimension is oriented vertically. The problem this presents in application to spectrophotometer, reflectometer, ellipsometer, polarimeter or the like systems is that as an arc-lamp ages, the focal point from which a beam of electromagnetic radiation therefrom originates moves. This effectively changes the angle-of-incidence of the beam to a sample surface. As said angle-of-incidence must be known to enable valid analysis of data corresponding to reflected or transmitted electromagnetic radiation from or through said sample, it can be appreciated that where arc-lamps are mounted with their elongated dimension oriented vertically in spectrophotometer, reflectometer, ellipsometer, polarimeter or the like systems, problems are present.
One solution is to use a sequence of mirrors to rotate the locus of the elongated dimension of an arc-lamp 90 degrees. Then as the origin of the beam changes, the angle-of-incidence does not change. Rather a the beam impinges on a sample surface at a laterally slightly different point. Another approach is to ignore manufacturer recommendations and mount the arc-lamp so that elongated dimension thereof projects horizontally. However, when this is done it is found that the upper inner surface of the arc-lamp becomes progressively less transparent because of sputtered depositions thereon. The lower inner surface of the horizontally oriented arc-lamp, however, remains relatively unaffected.
The following patents all describe ellipsometer or the like systems which comprise a plurality of reflective means and/or means for directing beams:                U.S. Pat. No. 5,969,818 to Johs et al.;        U.S. Pat. No. 5,764,365 to Finarov;        U.S. Pat. No. 5,343,293 Berger et al.;        U.S. Pat. No. 4,647,207 to Bjork et al.;        U.S. Pat. No. 3,874,797 to Kasai;        U.S. Pat. RE38,253 to Finarov;        U.S. Pat. No. 6,714,301 to Otsuki et al.;        U.S. Pat. No. 6,753,962 to Opsal et al.;        U.S. Pat. No. 5,229,833 to Stewart;        U.S. Pat. No. 4,790,659 to Erman et al.;        U.S. Pat. No. 4,210,401 to Batten;        U.S. Pat. No. 5,963,327 to He et al.;        U.S. Pat. No. 6,795,184 to Herzinger at al.        U.S. Pat. No. 4,681,450 to Azzam;        U.S. Pat. No. 4,332,476 to Stenberg et al.        Published Application No. US 2004/0085538 A1 by Hovinen et al.;        Published Application No. US 2002/0159063 A1 by Kanzaki.        
Even in view of the prior art need remains for improved means of providing beams for horizontally oriented arc-lamps in spectrophotometer, reflectometer, ellipsometer, polarimeter Mueller Matrix measuring, or the like system.